1. Field of the Invention
The present invention relates to improvements in rotors for DC motors.
2. Description of the Prior Art
As described in Japanese Published Unexamined Patent Application (OPI) No. 221551/1986, prior art DC motors have rotors consisting of an axial lamination of core sheets of soft iron plate having a plurality of radial and inward slits through which armature coils are wound. The lamination of core sheets is mounted on an armature rotary axis. Such a prior art rotor has a so-called semi-closed structure in which the opening of the slits in each core sheet are partially closed by a folding portion. The reason why the opening of the slits in each core sheet is half closed is that this semi-closed structure provides an advantageous magnetic circuit.
The prior art rotor has a lamination of a plurality of core sheets of soft iron plate because it is difficult to form such a semi-closed rotor from thin electromagnetic steel plates by folding the opening of slits in each core sheet. However, the prior art rotor comprising a lamination of core sheets of soft iron plate is disadvantageous in that the iron loss cannot be decreased, thus making it impossible to improve the motor output.